You'll be happy to know the RP goes underway soon- Nobody's character will soon be set up. In terms of their base of operations, a couple of locations of bases near airstrips of some sort spring to mind- with myself inclined to the first:

A) An abandoned airbase built on artificial ground off Bouvet Island, a Norwegian depedency in the South Atlantic. It is the furthest island from any major land mass in the world, and is fully in Scimitar's control. It's in the middle of nowhere, and as a result, is perfect for training- as well as the glacier offering plenty of wingsuit opportunities and Arctic-based training.

B) A large hangar somewhere on Singapore's Changi Airport, away from most of the airline terminals and built in such a way that it is impossible almost to figure out what is there. A C130, as well as a variety of kit means that the team is rapidly deployable to almost any location, hidden in plain sight and inversely from Bouvet, is in the midst of a population centre. Little training facilities, but has this nice accessible feel to it near civilization, a significant one.